There are a broad array of electrical and electronic devices which incorporate components that deliver acoustic energy into the ear canal of a listener. Hearing aids and so called “ear bud” headphones for cell phones, portable audio players, etc. are but representative examples of such devices. Several configurations of ear fittings exist for delivering acoustic energy directly to the ear canal, including configurations known as open ear fittings, open fit, closed ear fittings, foam fittings etc. Examples of hearing aid devices some of which utilize such ear fittings include: Behind the Ear (BTE), In the Ear (ITE), In the Canal (ITC), Completely in the Canal (CIC), Over the Ear (OTE) or Open-Fit devices. Each of the fitting devices is known to involve compromises of acoustic performance, user comfort and other criteria.
Open-Fit hearing aids or open-ear fittings may comprise a shaped fitting for placement within the ear canal. The fitting itself may include a polymeric ear tip that is sufficiently elastomeric to conform to an ear canal. Open ear fittings are so named because they provide some opening between the ear canal and the environment.
Such openings may help to reduce an undesirable acoustic characteristic known as the occlusion effect. The occlusion effect causes the listener to perceive low frequency or base sounds to be louder and possibly more distorted. The sources of the sounds that are typically associated with the occlusion effect include the user's own voice, chewing, other jaw movement etc. Open ear fittings reduce this effect because the open areas within the fitting allow some of the acoustic energy delivered to the ear canal to escape. The increased air exchange between the ear canal and the environment provided by such open ear fittings may also improve user comfort. However, these open areas or pathways, while providing some advantage may promote other undesirable acoustic effects.
The open areas provided in open ear fittings may, however, cause parasitic or sound distorting resonances. Distortions at certain frequency ranges of around 1 to 3.5 kHz are particularly important and could result in noticeably degraded acoustic performance. Moreover, some acoustic energy may be lost as it escapes through the open area. Typically, isolation from external environment is poor allowing external sound to leak around the fitting directly into the ear canal.
A need clearly exists for an open ear fitting which has improved acoustic performance while maintaining user comfort.